Motorized vehicles are generally slowed and/or stopped with hydraulic brake systems. A basic brake system generally includes a brake pedal, a master cylinder, brake fluid conduits arranged in two similar but separate brake circuits, and wheel brakes in each circuit. The driver of the vehicle operates the brake pedal which is connected to the master cylinder. When the brake pedal is depressed, the master cylinder generates hydraulic forces in both brake circuits by pressurizing brake fluid. The pressurized fluid travels through the fluid conduit in both circuits to actuate brake cylinders at the wheels to slow or stop the vehicle. Generally, when the brake pedal is first compressed, there is little resistance to the initial movement of the brake pedal during depression. As the brake pedal is further depressed by a user, the force required for further pedal depression increases. Generally, the force required to initially depress the brake pedal to the force required for full depression of the brake pedal is a non-linear force curve.
Recently, advanced vehicle braking systems, such as, for example, electro-hydraulic braking systems, have been designed. In such systems, the master cylinder is typically a separate component from the vehicle's brakes. In such systems, an electronic control unit is provided to respond to brake demand signals and to control the operation of pumps which apply pressurized brake fluid to the wheel brakes of each brake circuit. As such, when the brake pedal is actuated, it does not typically directly actuate the wheel brakes, but rather acts to generate a brake demand signal which is used as an input signal to an electronically-controlled vehicle braking system. One disadvantage of such systems is that the brake pedal does not feel or behave like a brake pedal in a hydraulic braking system (e.g., in a non-linear, progressively increasing pedal force).
Non-limiting examples of existing prior art pedal feel simulator devices for vehicle braking systems are described in U.S. Pat. Nos. 6,347,518 and 6,746,088, US Publication Nos. 2003/0205932, US 2014/0138888, US 2014/0159473, and WO 2014/145447A1, all of which are incorporated herein by reference. These prior art simulator devices are generally complicated systems and cannot be easily customized for a particular use.
A need has been identified for a spring system that can be used in a hydraulic and/or electro-hydraulic vehicle braking system which can simulate the feel of a traditional brake pedal as experienced in a conventional hydraulic vehicle braking system, and which can easily be customized for different types of brake systems or for other types of uses that benefit from a non-linear force verse stroke profile for a spring system.